The Lexmark T650 series does not use corona wires. Some possible causes of light images are:

a) The darkness is adjustable - on the printer select: menu : settings : quality menu : toner darkness. A larger number produces a darker image.

b) The toner cartridge might be empty. If this is the case, shaking these cartridges can reposition enough toner to provide a short term quality improvement.

c) Light images may be caused by an old OPC (Optical Photo Conductor) roller that is built into the disposable toner cartridge.